Engine oil deteriorates in various ways as it is used in an engine over time. Degradation sources include thermal stresses, tribological interactions (or the interaction of adjacent surfaces under relative motion), and byproducts of combustion. Evaluators of engine oil degradation have, heretofore, considered various key oil properties separately, if at all.
While one evaluator may measure only viscosity of an oil sample, for instance, and conclude based solely on that measurement whether the oil has useful life remaining, another may, measure only a total acid number (or TAN; the amount of potassium hydroxide in milligrams that is needed to neutralize the acids in one gram of oil), and base their conclusion solely on that measurement.
Determinations about overall oil quality based on only one parameter (e.g., viscosity or TAN) have inherent shortcomings because oil deteriorates in many distinct ways. Although an oil sample may have an undesirably high TAN, for example, the oil can be satisfactory overall for continued use. And while a sample may have a healthy viscosity, the oil can be unsatisfactory overall for continued use.
There is a need for technology that automatically generates an objective indication of oil quality and remaining oil life, if any, based on multiple preselected key oil properties taken together.